The Balance and Imbalance of Microbial Communities: Oral-Gut Microbiota and Colorectal Cancer.

The microbiome is a significant multimicrobial community that coexists with the human body in a symbiotic relationship. These microbial communities participate in mechanisms, such as defense against infections, absorption of nutrients, and maintenance of internal homeostasis. Although the microbiome is involved in physiological processes that are beneficial to host health, it can also lead to serious problems. Despite being far apart, the oral cavity and colon are both highly colonized by different microbial communities. Studies have shown that oral bacteria can migrate to and colonize the colon, which is most evident in diseases such as periodontitis. These oral pathogenic bacteria, which contain a large number of carcinogenic factors such as Fusobacterium nucleatum and Porphyromonas gingivalis, can penetrate the large intestine and cause intestinal microbial imbalance and dysfunction, thereby stimulating carcinogenesis. Increasing evidence suggests that oral microbiota, especially certain periodontal pathogens, may be used as biomarkers for colorectal cancer (CRC). Understanding the exact mechanisms of microbiome interactions and their impact on CRC will provide future opportunities for the prevention and treatment of colorectal cancer, and is an important prerequisite for its use as a precise noninvasive biomarker, which is crucial for the early detection of CRC. This review aims to summarize the current research status of oral microbiota, gut microbiota, and their association with CRC, and to evaluate the effectiveness of oral microbiome-derived biomarkers.